1. Technical Field
This invention relates in general to the communication from a casing annulus to the outer wellhead housing, and more particularly to the monitoring of casing annulus pressure, the injection of drill cuttings generated from drilling a subsea well, or the injection of a heavy fluid into the casing annulus to reduce the casing annulus pressure.
2. Background of the Invention
A subsea well that is capable of producing oil or gas will have an outer or low pressure wellhead housing secured to a string of conductor pipe which extends some short depth into the well. An inner or high pressure wellhead housing lands in the outer wellhead housing. The high pressure wellhead housing is secured to an outer string of casing, which extends through the conductor pipe to a deeper depth into the well. Depending on the particular conditions of the geological strata above the target zone (typically, either an oil or gas producing zone or a fluid injection zone), one or more additional casing strings will extend through the outer string of casing to increasing depths in the well until the well is to the final depth.
The last string of casing extends into the well to the final depth, this being the production casing. The strings of casing between the first casing and the production casing are intermediate casing strings. When each string of casing is hung in the wellhead housing, a cement slurry is flowed through the inside of the casing, out of the bottom of the casing, and back up the outside of the casing to a predetermined point.
Virtually all producing wells monitor pressure in the annulus flow passage between the strings of casings. Normally there should be no pressure in the annulus between each string of casing because the annular space between each string of casing and the next larger string of casing is ordinarily cemented at its lower end and sealed with a packoff. If pressure increased within an annulus between the strings of casings, it would indicate that a leak exists in one of the strings of casing. The leak could be from several places. Regardless of where the leak is coming from, pressure build up in the annulus could collapse a portion of the production casing, compromising the structural and pressure integrity of the well. For this reason, operators monitor the pressure in the annulus between the production casing and the next larger string of casing in a well.
It is advantageous to be able to have a way to efficiently communicate with a casing inside of a high pressure or inner wellhead housing. Operators need the capability to pump down a heavy fluid into the casing annulus of a well in order to reduce casing annulus pressure. It is also desirous for operators to monitor an annular pressure between the high pressure wellhead housing and a string of casing positioned inside of the wellhead housing. Furthermore, operators also desire an efficient way to inject xe2x80x9ccuttingsxe2x80x9d into the casing annulus of the well.
When a subsea well is drilled, cuttings, which are small chips and pieces of various earth formations, will be circulated upward in the drilling mud to the drilling vessel. These cuttings are separated from the drilling mud and the drilling mud is pumped back into the well, maintaining continuous circulation while drilling. The cuttings in the past have been dumped back into the sea or conveyed to a disposal site on land.
While such practice is acceptable for use with water based drilling muds, oil based drilling muds have advantages in some earth formations. The cuttings would be contaminated with the oil, which would result in pollution if dumped back into the sea. As a result, environmental regulations now prohibit the dumping into the sea of cuttings produced from oil based muds.
There have been various proposals to dispose of the oil based cuttings. One proposal is to inject the cuttings back into a well. The well could be the well being drilled, or the well could be an adjacent subsea well. Various proposals in patents suggest pumping the cuttings down an annulus between two sets of casing into an annular space in the well that has a porous formation. The cuttings would be ground up into a slurry and injected into the porous earth formation. Subsequently, the well receiving the injected cuttings would be completed into a production well.
U.S. Pat. No. 5,085,277, Feb. 4, 1992, Hans P. Hopper, shows equipment for injecting cuttings into an annulus surrounding casing. The equipment utilizes piping through the template or guidebase and through ports in specially constructed inner and outer wellhead housings. Orientation of the inner wellhead housing with the outer wellhead housing is required to align the ports. In the ""277 patent, orientation is not discussed, but it appears that it would require rotating the string of casing attached to the inner wellhead housing, which would be difficult. Another known injection system avoids having to rotate the string of casing attached to the inner wellhead housing by running the casing first, supporting it on a landing ring, then on a second trip running the inner wellhead housing assembly. The inner wellhead housing assembly has a port which is oriented. The inner wellhead housing is then secured to the string of casing. While workable, this requires two trips to run the inner wellhead housing and string of casing, which is time consuming for deep water drilling.
U.S. Pat. No. 5,662,129, Sep. 2, 1997, Stanley Hosie, shows equipment with specially manufactured extensions attached between the lower portions of both the inner and outer wellhead housings and the upper portions of the casings hanging therefrom. Each of the extensions have ports that must align in order for the cuttings to communicate through the inner and outer wellhead housings to an annular space inside of the inner wellhead housing. A swivel joint on the extension of the inner wellhead housing supports the casing hanging therefrom while allowing rotation of the inner casing above the swivel joint for aligning ports extending through each of the inner and outer wellhead housings.
U.S. Pat. No. 6,394,194, May 28, 2002, Michael Queen et al., shows equipment with a port formed in a collar that aligned with a passage in an inner wellhead housing above the outer wellhead housing. Having the communication port in the collar positioned above the outer wellhead housing was one way to remove the necessity of aligning a port on the inner wellhead housing with a port on the outer wellhead housing. The collar, however, had to be aligned with the passageway opening to the outer surface of the inner wellhead housing, and then the injector system had to align with the port formed in the collar. This necessitated the use of two brackets that had to land around the inner wellhead housing after the inner wellhead housing had landed.
U.S. Pat. No. 5,366,017, Nov. 22, 1994, Robert K. Voss, Jr., and U.S. Pat. No. 5,544,707, Aug. 13, 1996, Hans P. Hopper et al., both show equipment for monitoring casing annulus pressure. The inventions disclosed in both of these patents show equipment that has the casing annulus pressure communicating to a point above the high pressure wellhead housing on the exterior of a tree assembly that has landed on the high pressure wellhead housing. Various systems have been utilized in order to prevent the casing annulus from communicating until the tree assembly lands on the high pressure wellhead housing. With the equipment shown in the Hopper and Voss patents, it is difficult to monitor the casing annulus pressure before the tree assembly lands.
U.S. Pat. No. 6,186,239, Feb. 13, 2001, Noel A. Monjure et al., shows equipment for circulating heavy fluids into an annulus formed between casing strings in order to relieve casing pressure due to leaks. The invention disclosed in the Monjure ""239 patent shows injecting heavy fluids into a well by lowering a flexible hose into an annulus between casing strings. Heavy fluids are pumped through the hose and into the annulus for well fluid displacement when the pressure builds up in the annulus between casing strings due to leaks in the casing.
A subsea wellhead assembly has the capabilities of communicating from the outer surface of an outer, low pressure wellhead housing to an annulus located inside of an inner, high pressure wellhead housing. The subsea wellhead has an outer wellhead housing and an inner wellhead housing. The inner wellhead housing has a bore and a lower portion that lands in the outer wellhead housing. A pair of seals between the outer and inner wellhead housings define an annular chamber when the inner wellhead housing lands in the outer wellhead housing. The outer wellhead housing has a communication port extending through a side of the outer wellhead housing. The inner wellhead housing has a passageway extending from the annular chamber to the bore of the inner wellhead housing for communicating with a casing annulus.
The casing annulus located circumferentially inward of the inner wellhead housing is in communication with the annular chamber on the outside of the inner wellhead housing. The annular chamber is in communication with the outer surface of the outer wellhead housing through the communication port. Therefore, the casing annulus is in communication with the outer surface of the wellhead housing. The operator can monitor casing annulus pressure, inject heavy fluid into the casing annulus, or inject cuttings from the outer surface of the outer wellhead housing to the casing annulus.
In the preferred embodiment, a wear resistant surface is formed on the outer surface of the inner wellhead housing. Preferably, the wear resistant surface is located axially at substantially the same position as the communication port. The wear resistant surface can reduce the damage to the surface of the inner wellhead housing when injecting cuttings from the communication port.
In the preferred embodiment, the subsea wellhead assembly also has an injection mechanism for injecting a slurry of cuttings or a heavy fluid into the well. The injection mechanism typically has a frame with a manifold, or support member, that extends partially around the outer wellhead housing. The injection mechanism also has a flowline connector for communicating with the communication port. A flowline may communicate a slurry of cuttings or a heavy fluid to the flowline connector from another location. The flowline connector typically has an end that operably seals and engages with the communication port and an end for receiving the slurry of cuttings or the heavy fluid from a flowline. The injection mechanism also has a plurality of lock members on the manifold, or support member, that move into engagement with a mating profile on an exterior surface of the outer wellhead housing. In the preferred embodiment, the frame aligns to receive the outer wellhead housing with a pair of sleeves that slidingly receive a pair of guidelines.